/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package java.util.concurrent;

import java.util.List;
import java.util.Collection;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;

/**
 * An {@link Executor} that provides methods to manage termination and
 * methods that can produce a {@link Future} for tracking progress of
 * one or more asynchronous tasks.  
 *
 * <p>
 * An <tt>ExecutorService</tt> can be shut down, which will cause it
 * to stop accepting new tasks.  After being shut down, the executor
 * will eventually terminate, at which point no tasks are actively
 * executing, no tasks are awaiting execution, and no new tasks can be
 * submitted.
 *
 * <p> Method <tt>submit</tt> extends base method {@link
 * Executor#execute} by creating and returning a {@link Future} that
 * can be used to cancel execution and/or wait for completion.
 * Methods <tt>invokeAny</tt> and <tt>invokeAll</tt> perform the most
 * commonly useful forms of bulk execution, executing a collection of
 * tasks and then waiting for at least one, or all, to
 * complete. (Class {@link ExecutorCompletionService} can be used to
 * write customized variants of these methods.)
 *
 * <p>The {@link Executors} class provides factory methods for the
 * executor services provided in this package.
 *
 * <h3>Usage Example</h3>
 *
 * Here is a sketch of a network service in which threads in a thread
 * pool service incoming requests. It uses the preconfigured {@link
 * Executors#newFixedThreadPool} factory method:
 *
 * <pre>
 * class NetworkService {
 *    private final ServerSocket serverSocket;
 *    private final ExecutorService pool;
 *
 *    public NetworkService(int port, int poolSize) throws IOException {
 *      serverSocket = new ServerSocket(port);
 *      pool = Executors.newFixedThreadPool(poolSize);
 *    }
 * 
 *    public void serve() {
 *      try {
 *        for (;;) {
 *          pool.execute(new Handler(serverSocket.accept()));
 *        }
 *      } catch (IOException ex) {
 *        pool.shutdown();
 *      }
 *    }
 *  }
 *
 *  class Handler implements Runnable {
 *    private final Socket socket;
 *    Handler(Socket socket) { this.socket = socket; }
 *    public void run() {
 *      // read and service request
 *    }
 * }
 * </pre>
 * @since 1.5
 * @author Doug Lea
 */
public interface ExecutorService extends Executor {

    /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be
     * accepted. Invocation has no additional effect if already shut
     * down.
     * @throws SecurityException if a security manager exists and
     * shutting down this ExecutorService may manipulate threads that
     * the caller is not permitted to modify because it does not hold
     * {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
     * or the security manager's <tt>checkAccess</tt>  method denies access.
     */
    void shutdown();

    /**
     * Attempts to stop all actively executing tasks, halts the
     * processing of waiting tasks, and returns a list of the tasks that were
     * awaiting execution. 
     *  
     * <p>There are no guarantees beyond best-effort attempts to stop
     * processing actively executing tasks.  For example, typical
     * implementations will cancel via {@link Thread#interrupt}, so if any
     * tasks mask or fail to respond to interrupts, they may never terminate.
     *
     * @return list of tasks that never commenced execution
     * @throws SecurityException if a security manager exists and
     * shutting down this ExecutorService may manipulate threads that
     * the caller is not permitted to modify because it does not hold
     * {@link java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
     * or the security manager's <tt>checkAccess</tt> method denies access.
     */
    List<Runnable> shutdownNow();

    /**
     * Returns <tt>true</tt> if this executor has been shut down.
     *
     * @return <tt>true</tt> if this executor has been shut down
     */
    boolean isShutdown();

    /**
     * Returns <tt>true</tt> if all tasks have completed following shut down.
     * Note that <tt>isTerminated</tt> is never <tt>true</tt> unless
     * either <tt>shutdown</tt> or <tt>shutdownNow</tt> was called first.
     *
     * @return <tt>true</tt> if all tasks have completed following shut down
     */
    boolean isTerminated();

    /**
     * Blocks until all tasks have completed execution after a shutdown
     * request, or the timeout occurs, or the current thread is
     * interrupted, whichever happens first.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return <tt>true</tt> if this executor terminated and <tt>false</tt>
     * if the timeout elapsed before termination
     * @throws InterruptedException if interrupted while waiting
     */
    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;


    /**
     * Submits a value-returning task for execution and returns a Future
     * representing the pending results of the task. 
     *
     * <p>
     * If you would like to immediately block waiting
     * for a task, you can use constructions of the form
     * <tt>result = exec.submit(aCallable).get();</tt>
     *
     * <p> Note: The {@link Executors} class includes a set of methods
     * that can convert some other common closure-like objects,
     * for example, {@link java.security.PrivilegedAction} to
     * {@link Callable} form so they can be submitted.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws NullPointerException if task null
     */
    <T> Future<T> submit(Callable<T> task);

    /**
     * Submits a Runnable task for execution and returns a Future 
     * representing that task that will upon completion return 
     * the given result
     *
     * @param task the task to submit
     * @param result the result to return
     * @return a Future representing pending completion of the task,
     * and whose <tt>get()</tt> method will return the given result
     * upon completion.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws NullPointerException if task null     
     */
    <T> Future<T> submit(Runnable task, T result);

    /**
     * Submits a Runnable task for execution and returns a Future 
     * representing that task.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task,
     * and whose <tt>get()</tt> method will return <tt>null</tt>
     * upon completion.
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws NullPointerException if task null
     */
    Future<?> submit(Runnable task);

    /**
     * Executes the given tasks, returning their results
     * when all complete.
     * Note that a <em>completed</em> task could have
     * terminated either normally or by throwing an exception.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     * @param tasks the collection of tasks
     * @return A list of Futures representing the tasks, in the same
     * sequential order as produced by the iterator for the given task
     * list, each of which has completed.
     * @throws InterruptedException if interrupted while waiting, in
     * which case unfinished tasks are cancelled.
     * @throws NullPointerException if tasks or any of its elements are <tt>null</tt>
     * @throws RejectedExecutionException if any task cannot be scheduled
     * for execution
     */

    <T> List<Future<T>> invokeAll(Collection<Callable<T>> tasks)
        throws InterruptedException;

    /**
     * Executes the given tasks, returning their results
     * when all complete or the timeout expires, whichever happens first.
     * Upon return, tasks that have not completed are cancelled.
     * Note that a <em>completed</em> task could have
     * terminated either normally or by throwing an exception.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     * @param tasks the collection of tasks
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return A list of Futures representing the tasks, in the same
     * sequential order as produced by the iterator for the given
     * task list. If the operation did not time out, each task will
     * have completed. If it did time out, some of thiese tasks will
     * not have completed.
     * @throws InterruptedException if interrupted while waiting, in
     * which case unfinished tasks are cancelled.
     * @throws NullPointerException if tasks, any of its elements, or
     * unit are <tt>null</tt>
     * @throws RejectedExecutionException if any task cannot be scheduled
     * for execution
     */
    <T> List<Future<T>> invokeAll(Collection<Callable<T>> tasks, 
                                  long timeout, TimeUnit unit) 
        throws InterruptedException;

    /**
     * Executes the given tasks, returning the result
     * of one that has completed successfully (i.e., without throwing
     * an exception), if any do. Upon normal or exceptional return,
     * tasks that have not completed are cancelled.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     * @param tasks the collection of tasks
     * @return The result returned by one of the tasks.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks or any of its elements
     * are <tt>null</tt>
     * @throws IllegalArgumentException if tasks empty
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     * for execution
     */
    <T> T invokeAny(Collection<Callable<T>> tasks)
        throws InterruptedException, ExecutionException;

    /**
     * Executes the given tasks, returning the result
     * of one that has completed successfully (i.e., without throwing
     * an exception), if any do before the given timeout elapses.
     * Upon normal or exceptional return, tasks that have not
     * completed are cancelled.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     * @param tasks the collection of tasks
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return The result returned by one of the tasks.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks, any of its elements, or
     * unit are <tt>null</tt>
     * @throws TimeoutException if the given timeout elapses before
     * any task successfully completes
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     * for execution
     */
    <T> T invokeAny(Collection<Callable<T>> tasks, 
                    long timeout, TimeUnit unit) 
        throws InterruptedException, ExecutionException, TimeoutException;

}
